This application claims the priority benefit of Taiwan application serial no. 88222560, filed Dec. 18, 1999.
1. Field of Invention
The present invention relates to the light source of a scanner. More particularly, the present invention relates to an installation for improving a scanning range of a scanner along an axial direction of a light source.
2. Description of Related Art
In general, a scanning system can be roughly classified as a reflective type or a light-penetrating type. In the reflective scanning system, a document is placed over a transparent glass panel. Light from a light source travels through the transparent glass panel and impinges upon the document. The light is reflected back from the document to reach an optical sensor after passing through a set of optical elements. The optical sensor for forming a scan image, for example, can be a charge couple device (CCD). In the light-penetrating scanning system, the document is also placed on top of a transparent glass panel. However, light from a light source has to pass through the document, the transparent glass panel and a set of optical elements before arriving at the optical sensor.
Hence, both the reflective and the transparent type of scanning system operate on similar principles. In a reflective scanning system, brightness variation of reflected light from a document is gauged to produce a scan image. On the other hand, in a transparency scanning system, brightness variation of light after passing through the document is gauged to produce a scan image.
However, the conventional linear light source of a scanner has one major drawback. Brightness level close to the mid-section along the axial direction of a light source is higher than the brightness level on each side. Hence, image produced by the light source is brighter in the middle. Since a scanner works according to differences in brightness level, capacity for detecting brightness contrast near both ends of the light axis is lower. If the variation in brightness level along the axial direction of the light source is large, a section close to both ends of the light axis is unsuitable for forming any images.
Several means have been proposed to reduce brightness variation along the axial direction of the light source, several means are proposed. For example, in an invention described in Taiwan Patent No. 244013 titled xe2x80x98Improved brightness compensation of an optical scanner through a modified lamp shade structurexe2x80x99, brightness variation along the axial direction of a light source is improved by modifying the lampshade.
In another invention described in Taiwan Patent No. 204363 titled xe2x80x98Image-forming optical system for a scannerxe2x80x99, the external structure of the lamp tube is directly modified. For example, two lamp tubes are used instead of one so that compensatory back reflection is increased. Consequently, brightness levels between the central and the side portions along the axial direction of the lamp tubes are almost identical when onto a document. However, the invention demands major modifications of many structural elements. Hence, cost of production is high.
In another invention described in Taiwan Patent No. 352886 titled xe2x80x98A lens structure and its integration with an image-reading devicexe2x80x99, a method of improving brightness level along the axial direction of a light source is proposed. By changing the degree of reflectivity of a coated film on the reflecting lens inside a scanner, brightness level variation is reduced. However, the reflectivities of more than one reflecting lens need to be modified, thereby increasing the production cost necessary to achieve the results.
In short, the smaller the variation in brightness level along the axial direction of a light source, the better the scanning width of a document and brightness contrast are. Although all the conventional methods are capable of reducing brightness variation along the axial direction of a light source, major structural modification of components are unnecessary.
Accordingly, one object of the present invention is to modify a component in a scanner so that the useful range along the axial direction of a light source is increased. The component is a light-channeling panel and the modification is a variation of light transparency across the surface of the light-channeling panel.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an installation for increasing the useful range along the axial direction of a light source. The installation includes a linear light source and a light-channeling panel. The linear light source has a light axis whose brightness near the mid-portion is higher than the brightness level on either side. The light source provides a necessary beam of light for image scanning by the scanner.
The light-channeling panel is adjacent to the linear light source and is capable of concentrating more light to the end sections rather than the mid-portion of the light axis. The light-channeling panel is made from a plurality of panels, each being made from a panel material having a light transparency different from the others. The light transparency of the light-channeling panel near the central section of the light axis is lower than the light transparency at the end sections of the light axis. Hence, after light from the linear light source passes through the light-channeling panel, a band of light having more homogenous brightness level than the linear light source is produced.
This invention also provides a second installation for increasing the useful range along the axial direction of a light source, which installation includes a linear light source, a light-channeling panel, an optical transmission system and an optical sensor. The linear light source has a light axis whose brightness level near the middle portion is higher than the brightness level on each side. The light source provides a necessary beam of light for scanning a document by the scanner. The light-channeling panel is adjacent to the linear light source and is capable of concentrating more light in the end sections rather than the middle of the light axis. The light-channeling panel is formed by attaching a plurality of panels with each panel made from a material having a different light transparency. The light transparency of the light-channeling panel near the central section of the light axis is lower than the light transparency at the end sections of the light axis. Hence, after light from the linear light source passes through the light-channeling panel, a band of light having a more homogenous brightness level than the linear light source is produced. The optical transmission system transmits the light that has passed through the document or the light that has reflected from the document. The optical sensor picks up the light from the optical transmission system for producing a scan image.
This invention also provides a third installation for increasing the useful range along the axial direction of a light source that includes a linear light source, a light-channeling panel and a contact image sensor (CIS). The linear light source has a light axis whose brightness level near the middle portion is higher than the brightness level on each side. The light source provides a necessary beam of light for scanning a document by the scanner. The light-channeling panel is adjacent to the linear light source and is capable of concentrating more light near the end of the light axis. The light-channeling panel is formed by attaching a plurality of panels, each panel being made from a panel material having a light transparency different from the others. The light transparency of the light-channeling panel near the central section of the light axis is lower than the light transparency at the end sections of the light axis. Hence, after light from the linear light source passes through the light-channeling panel, a band of light having more homogenous brightness level than the linear light source is produced. The contact image sensor picks up the light that has passed through the document or the light that has reflected from the document for producing a scan image.
In brief, this invention homogenizes the brightness level along the light axis by changing the light transparency across the surface of the light-channeling panel.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.